I've just repaired half a dozen Apple IIc motherboards. These are quite notorious to repair, as all the DRAMs are soldered in. So I had to make a diagnostics EPROM which would pinpoint the bad DRAM(s) even when the machine was unable to do anything and even the text screen was corrupted. I might post that EPROM image later if there is any interest - I think diagnostics EPROMs should already exist somewhere in the web, but they eluded me, too many dead links and stale posts. So maybe my work making my own was redundant. But it took me only 20 minutes to derive it from the source code I already had (for the diagnostics page in the PROMs of my famous Apple-1 kits). Less time than I wasted searching for a ready made solution on the web.
Here is the fundamental problem / pitfall with the Apple IIc (BEWARE !):
It seems the machine does not do a POST to check the integrity of the RAM and the ROM before it attempts to boot a floppy disk. Alas, certain kinds of DRAM faults make the boot fail with the message "check disk drive". Which sets in motion a tinkering process (owners taking the Apple IIc apart and messing around with disk drives) which ultimately leads to the destruction of the IWM ("Integrated Woz Machine", the Apple IIc floppy disk controller). Because having no known good Apple IIc disk drive in hand, they plug in a Disk II drive which uses the same 20 pin flat band cable and connector. Alas, the pinout is different. Pooof ! The IWM is dead. Now the poor Apple IIc has two ailments: bad DRAM and the bad IWM.
This did not happen to me, as I use to check schematics before working on anything, but I bought those decrepit Apple IIc at flea markets for a song, maybe 20+ years ago, and lo and behold, all of them not only had one or more bad DRAM chips, but half of them (three) also had blown up IWMs.
So, this story told (hope it helps people to avoid blowing up IWMs), I need 3 IWMs which work but can't find any source. The usual suspects (Chip brokers) list IWMs but I don't want to waste my time with them - they all have minimum orders and I don't need 100 IWMs.
Maybe somebody has an idea where IWMs can be found (other than destroying another Apple IIc or early Mac). I dimly seem to remember there was a card for the Apple II which had one, but I'm not sure if this was the IWM or the SWIM.
Any hint is much appreciated !
(Oh, I also would need the plastic face plate for an Apple IIc disk drive and the screws, as one of the mine came without it - seems the ex owner was too frustrated to put it together again after his attempts to 'fix' it failed. Oh, of course he blew the IWM up, too.)
- Uncle Bernie
P.S.: don't forget to tell me if there could be a need for the diagnostics EPROM.